Switched-Mode Power Controller Startup With PWM-to-Valley Transition
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Solution Overview
Problem
Conventional quasi-resonant switched-mode power controllers face challenges in minimizing switching losses and achieving fast startup times while maintaining output voltage regulation, particularly in transitioning from startup to quasi-resonant modes of operation.
Innovation Solution
A multimode startup method is introduced, where the primary side controller generates a fixed switching frequency PWM signal with an incrementing duty-ratio during startup, transitioning to a quasi-resonant mode by reducing the number of valleys in off-times, facilitated by a uni-directional high-speed digital link between primary and secondary side controllers for precise voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional valley detection is used in quasi-resonant mode, then switching losses are minimized, but startup time increases
Solution Approach 1:
The controller dynamically switches between two operational modes: a fixed-frequency PWM mode for startup and a quasi-resonant valley-switching mode for steady-state operation. This dynamic mode transition allows the system to optimize for speed during startup and for efficiency during normal operation, resolving the contradiction between startup time and switching losses.
Solution Approach 2:
The system performs preliminary action by using fixed-frequency PWM switching during the startup phase to quickly establish output voltage before transitioning to valley detection. This preliminary fixed-frequency operation prepares the system for efficient quasi-resonant operation, effectively separating the startup speed requirement from the efficiency requirement.
2Loss of time
If fixed switching frequency PWM with incrementing duty-ratio is used during startup, then startup time is reduced, but switching losses increase
Solution Approach 1:
The system employs periodic fixed-frequency PWM switching during startup with incrementing duty-ratio to rapidly build output voltage. This periodic action is temporarily applied only during the startup phase, after which the system transitions to valley-based switching. The periodic nature allows predictable timing and controlled energy loss during the limited startup period.
Solution Approach 2:
Fixed-frequency PWM with incrementing duty-ratio serves as a preliminary action to quickly establish the output voltage during startup. This preliminary phase is intentionally designed to consume more energy but completes rapidly, after which the system transitions to the efficient valley-switching mode for sustained operation.
3Stability of the object's composition
If valley detection is reduced during transition, then smooth mode transition is achieved, but output voltage regulation precision temporarily decreases
Solution Approach 1:
The valley detection mechanism dynamically adjusts during the transition phase, reducing the number of valleys detected to facilitate smooth mode transition. This dynamic adjustment temporarily relaxes voltage regulation precision but enables stable mode switching, after which full valley detection resumes for precise regulation.
Solution Approach 2:
The system applies beforehand cushioning by temporarily reducing valley detection during the transition phase to prevent instability. This cushioning approach anticipates potential transition problems and mitigates them by relaxing control precision temporarily, ensuring stable mode switching before full precision regulation is restored.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables faster startup times and efficient quasi-resonant operation by reducing switching losses and minimizing component stress, while ensuring smooth transitions and precise output voltage control.
Implementation Method 1
The inductive device magnetizes during the on-time and demagnetizes during the off-time
Implementation Method 2
the inductive and parasitic capacitance components induce a quasi-resonant oscillating signal that includes valleys at times when the voltage across the power switch is zero or minimum value
Data Source
AI summary
A switched-mode power controller includes a primary side controller circuit configured in a startup mode of operation to generate a fixed switching frequency pulse width modulation (PWM) signal with incrementing duty-ratio value. The PWM signal drives a main-switch that charges an inductive device with stored energy and discharges the stored energy into a capacitor on a secondary side to generate a power controller output voltage. Based on a comparison of the power controller output voltage with a reference voltage, the primary side controller circuit is configured to stop the incrementing of the duty-ratio of the PWM signal and begin a quasi-resonant mode of operation during which the primary side controller circuit reduces a number of valleys detected in one or more off-times of the main-switch in one or more respective main-switch switching periods.